120 lines
2.9 KiB
Go
120 lines
2.9 KiB
Go
//go:build !no_voice
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package voice
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import (
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"encoding/binary"
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"sync"
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"time"
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"github.com/tphakala/go-opus/opus"
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)
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const (
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sampleRate = 48000
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channels = 2
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// frameSamples and frameBytes are the sizes of 20ms of PCM.
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frameSamples = sampleRate / 50 * channels
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frameBytes = frameSamples * 2
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// cushion is how much is buffered before it is played, so that packets arriving unevenly do not make gaps.
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cushion = 3 * frameBytes
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// maxBuffered is how much is buffered before the oldest is dropped rather than fall behind.
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maxBuffered = 10 * frameBytes
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// maxLost is how many packets in a row are made up for.
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maxLost = 3
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)
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// speaker decodes and buffers what one user says, to be mixed into what is played.
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type speaker struct {
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mu sync.Mutex
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decoder *opus.Decoder
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pcm []int16
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buf []byte
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// playing is whether the cushion was buffered and what is left of it is being played.
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playing bool
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// seq is the sequence number of the last packet, and last when it arrived.
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seq uint16
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last time.Time
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}
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// newSpeaker returns a speaker whose first packet has the sequence number seq.
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func newSpeaker(seq uint16) (*speaker, error) {
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decoder, err := opus.NewDecoder(sampleRate, channels)
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if err != nil {
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return nil, err
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}
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// 120ms is the longest an Opus packet can be.
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return &speaker{decoder: decoder, pcm: make([]int16, 6*frameSamples), seq: seq - 1}, nil
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}
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// decode appends what packet decodes to, or a made up frame if it is nil.
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func (s *speaker) decode(packet []byte) error {
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pcm := s.pcm
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if packet == nil {
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pcm = pcm[:frameSamples]
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}
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n, err := s.decoder.Decode(packet, pcm)
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if err != nil {
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return err
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}
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for _, sample := range pcm[:n*channels] {
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s.buf = binary.LittleEndian.AppendUint16(s.buf, uint16(sample))
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}
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return nil
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}
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// write buffers the packet with the sequence number seq.
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func (s *speaker) write(seq uint16, packet []byte) error {
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s.mu.Lock()
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defer s.mu.Unlock()
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// Make up for the few packets that never arrived. One that arrives late or twice is not worth playing.
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gap := seq - s.seq
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if gap == 0 || gap > 1<<15 && time.Since(s.last) < time.Second {
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return nil
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}
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if gap > 1 && gap <= maxLost+1 {
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for range gap - 1 {
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if err := s.decode(nil); err != nil {
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return err
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}
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}
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}
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s.seq, s.last = seq, time.Now()
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if err := s.decode(packet); err != nil {
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return err
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}
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if len(s.buf) > maxBuffered {
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s.buf = s.buf[len(s.buf)-cushion:]
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}
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return nil
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}
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// mix adds what is buffered to output, once the cushion is.
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func (s *speaker) mix(output []byte) {
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s.mu.Lock()
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defer s.mu.Unlock()
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if s.playing = s.playing || len(s.buf) >= cushion; !s.playing {
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return
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}
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n := min(len(output), len(s.buf))
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for i := 0; i+1 < n; i += 2 {
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sum := int32(int16(binary.LittleEndian.Uint16(output[i:]))) + int32(int16(binary.LittleEndian.Uint16(s.buf[i:])))
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binary.LittleEndian.PutUint16(output[i:], uint16(max(-1<<15, min(1<<15-1, sum))))
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}
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s.buf = s.buf[n:]
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s.playing = len(s.buf) > 0
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}
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